Assembly comprising a thermoelectric element and a means for electrically connecting said thermoelectric element, module and thermoelectric device comprising such an assembly

ABSTRACT

An assembly of at least one thermoelectric element capable of generating an electric current under the effect of a temperature gradient exerted between two of its sides, referred to as the contact sides, and an electrical connection means is disclosed. The assembly includes a first deformable element electrically connecting the electrical connection means to the thermoelectric element, the first element including a first side linked to the electrical connection means and a second side linked to the thermoelectric element, the first side being deformable independently from the second side and vice versa, the assembly including a second deformable element forming a heat bridge between the first and second sides of the first element. A thermoelectric module including such an assembly and a thermoelectric device including such a module are also disclosed.

The present invention relates to an assembly including a thermoelectricelement and a means for the electrical connection of said thermoelectricelement. It also relates to a thermoelectric module, notably intended togenerate an electric current in a motor vehicle, including said assemblyand a thermoelectric device including said module.

Thermoelectric modules have hitherto been proposed which use elements,referred to as thermoelectric elements, allowing an electric current tobe generated in the presence of a temperature gradient between two oftheir opposite sides, referred to as the first and second contact sides,according to the phenomenon known by the name of the Seebeck effect.These devices include a stack of first tubes, intended for the flow ofexhaust gases of an engine, and second tubes, intended for the flow of aheat transfer fluid of a cooling circuit. The thermoelectric elementsare sandwiched between the tubes in such a way as to be subjected to atemperature gradient originating from the temperature difference betweenthe exhaust gases, which are hot, and the cooling fluid, which is cold.

The thermoelectric elements are arranged in pairs. The thermoelectricelements belonging to the same pair are electrically interconnected viaelectrical paths disposed on their first or on their second contactsides.

It is known to assemble the thermoelectric elements on the electricalpaths by means of a soldering procedure. During this procedure, theelectrical paths and the metal thermoelectric elements are made toexpand under the effect of the temperature before the positiveconnection is established. Once the electrical paths have reached thecorrect temperature, the positive connection is established and theassembly is cooled.

One disadvantage comes from the fact that the electrical paths andthermoelectric elements do not have the same thermal expansioncoefficient. The electrical paths thus contract more than thethermoelectric elements during cooling, which risks damaging thethermoelectric elements, notably by creating cracks and/or breaks intheir contact surfaces.

This risk also exists when the thermoelectric module in operation issubjected to a substantial temperature difference between its cold sideand its hot side, which is typically the case when the hot side of thedevice is subjected to temperatures above 250° C. On reaching thesetemperatures, the electrical paths positively connected to thethermoelectric element on the hot side expand more than those positivelyconnected to the thermoelectric elements on the cold side, which risksdamaging the thermoelectric elements in the same way as described above.

The invention aims to improve the situation.

The invention thus proposes an assembly of at least one thermoelectricelement capable of generating an electric current under the effect of atemperature gradient exerted between two of its sides, referred to asthe contact sides, and electrical connection means, notably intended toelectrically connect said thermoelectric element to anotherthermoelectric element.

According to the invention, said assembly furthermore includes a firstdeformable element electrically connecting the electrical connectionmeans to the thermoelectric element, said first element including afirst side linked to the electrical connection element and a second sidelinked to the thermoelectric element, said first side being deformableindependently from said second side and vice versa, the assemblyincluding a second deformable element implementing a heat bridge betweenthe first and second sides of the first element.

By means of the invention, when the assembly is subjected to substantialtemperature variations, the first and second deformable elements canfollow, on the one hand, the deformation of the connection means and, onthe other hand, the deformation of the thermoelectric element. When theelectrical connection means and the thermoelectric element contract andexpand differently, the deformable link means then absorbs thesevariations.

By making the deformation of the first side independent from that of thesecond side and vice versa, the contraction and expansion of theelectrical connection means are mechanically decoupled from those of thethermoelectric element. The risk of breaks or cracks between theelectrical connection means and the thermoelectric element is thuslimited.

The first and second sides of the first element are advantageouslyinterconnected via two lateral walls in such a way that the firstelement forms a tube, notably with flat sides. The lateral sides can bedeformed to follow, on the one hand, the deformations of the first sideof the first element and, on the other hand, the deformations of thesecond side of the first element.

According to one embodiment of the invention, the first element is agrid. The grid can be deformed locally to absorb the differentialexpansion forces between the connection means and the thermoelectricelement. The first element may also be a sheet of material.

The grid advantageously has a thickness of between 50 and 300 μm.

According to one aspect of the invention, the first element is made ofmetal, advantageously aluminum.

According to one aspect of the invention, the second element isplastically and/or elastically deformable.

The second element advantageously fills a volume delimited by the firstside, the second side and the lateral sides of the first element. Thesecond element is thus deformed with the first side of the first elementin a certain way in order to follow the deformation of the connectionmeans and with the second side of the first element in a different wayin order to follow the deformation of the thermoelectric element. In thecase of a tube, it is adapted to the shape assumed by the tube.

According to one aspect of the invention, the second element is made ofa non-solderable material.

According to one aspect of the invention, the second element is made ofgraphite. The second element is advantageously a sheet of graphite witha thickness of less than 1 mm.

According to one aspect of the invention, said first deformable elementis soldered to said thermoelectric element and/or to said electricalconnection means.

According to one aspect of the invention, the assembly includes a secondthermoelectric element, having two contact sides, said second side ofsaid first element also being linked to said second thermoelectricelement.

The invention also relates to a thermoelectric module including aplurality of assemblies as described above.

The invention also relates to a thermoelectric device, notably intendedto generate an electric current in a motor vehicle, including at leastone module as described above.

The attached figures will clearly explain how the invention can beimplemented. In these figures, identical references denote similarelements.

FIG. 1 shows a perspective view of an example of a thermoelectric deviceaccording to the invention, shown in an exploded view;

FIG. 2 is a schematic side view of a part of a thermoelectric moduleincluding a plurality of assemblies according to the invention in whicheach electrical connection means is connected to the two thermoelectricelements via two independent first elements;

FIG. 3 is a schematic view of a part of a thermoelectric moduleincluding two thermoelectric elements and an electrical connection meanswhich is connected to the two thermoelectric elements via a single firstelement;

FIG. 4 is a perspective view showing a deformable link means of theassembly according to the invention;

FIGS. 5a, 5b, 5c are side views of the assembly according to theinvention shown at ambient temperature before soldering (5 a), atsoldering temperature (5 b) and at ambient temperature after soldering(5 c).

As shown in FIG. 1, a device according to the invention includes thermalconduction means in contact with a hot or cold source such as aplurality of flow tubes 1 of a first fluid alternating with a pluralityof flow tubes 2 of a second fluid. Said tubes 1, 2 extend here parallelto one another in the same direction.

The flow tubes 1 of the first fluid are configured, for example, for theflow of a fluid, referred to as a hot fluid. This may involve exhaustgases of a motor vehicle combustion engine. The flow tubes 1 of thefirst fluid define one or more flow channels of the first fluid,referred to as hot channels. The flow tubes 2 of the second fluid areconfigured, for example, for the flow of a fluid, referred to as a coldfluid, having a temperature lower than the temperature of the firstfluid. This may involve a cooling liquid, such as a mixture of water andglycol, originating, for example, from a low-temperature cooling loop ofthe vehicle. The flow tubes 2 of the second fluid define one or moreflow channels of the first fluid, referred to as cold channels.

Here, there are three exhaust gas flow tubes 1 are five cooling liquidflow tubes 2.

Said device furthermore includes a plurality of elements, referred to asthermoelectric elements, capable of creating an electric current from atemperature gradient applied between two of their sides, referred to asthe first and second contact sides, provided in a heat exchangerelationship with said hot and cold channels.

This involves, for example, more or less parallelepiped-shaped elements4 (shown schematically in FIGS. 2, 3 and 4) generating an electriccurrent, according to the Seebeck effect. According to other embodimentsthat are not shown, the shape of the elements 4 is different, such ascylindrical. Such elements allow the creation of an electric current ina charge connected between said contact sides 3 a, 3 b,disposed oppositeone another. In a manner known to the person skilled in the art, suchelements are made, for example, from manganese silicide (MnSi).

Said flow tubes 1, 2 have, for example, a flattened section according toa direction of elongation, orthogonal to the direction of expansion ofthe tubes. Said flow tubes 1, 2 may thus be flat tubes. This means thatthey have two large parallel sides connected by small sides. Thethermoelectric elements 4 are in contact with one and/or the other ofthe flat sides of the tubes 1, 2 via their contact sides 3 a,3 b.

Said tubes 2 intended for the flow of the cold fluid are made, forexample, from aluminum and/or aluminum alloy. The tubes 1 intended forthe flow of the hot fluid are made, notably, from stainless steel. Theyare formed, for example, by profiling, welding and/or soldering.

Said device furthermore includes, for example, a collector plate 15 ateach of the ends of said flow tubes 1 of the first fluid. Said collectorplate 15 is provided with orifices 6 into which the ends of said flowtubes 1 of the first fluid are inserted.

Said device may also include collector boxes 7 in fluid communicationwith the end of said flow tubes 1 of the first fluid and fixed to thecollector plates 15 by means of screws 8. Said boxes include an aperture16 for the input and output of the first fluid.

Said flow tubes 2 of the second fluid may be provided on each of theirends with collectors 9 allowing communication of said flow tubes 2 ofthe second fluid and with a collector box, not shown, of the secondfluid via apertures 10 opening out onto a lateral side of the groupdefined by the stack of the flow tubes 1, 2 of the first and secondfluid.

As shown in FIG. 1, the thermoelectric elements are distributed inlayers 5 provided between the flow tubes 1 of the first fluid and theflow tubes 2 of the second fluid. Each layer 5 represents schematicallya plurality of thermoelectric elements disposed here in a rectangularshape. In the thermoelectric device, electrical links are establishedbetween the layers 5 of thermoelectric elements. An electricalconnector, not shown, allows the device to be connected to an externalelectric circuit.

Here, said thermoelectric device includes a plurality of electricmodules, each of the electric modules being formed from at least one ofsaid cold channels and one of said hot channels and from a plurality ofsaid thermoelectric elements 4 located between said cold channel andsaid hot channel.

The thermoelectric elements 4 may, for a first part, be elements of afirst type, referred to as P (denoted 4P in FIG. 2) allowing anelectrical potential difference to be established in one direction,referred to as positive, when they are subjected to a given temperaturegradient, and, for the other part, elements of a second type, referredto as N (denoted 4N in FIG. 2) allowing the creation of an electricalpotential difference in an opposite direction, referred to as negative,when they are subjected to the same temperature gradient.

The thermoelectric elements applied to the same tube 1, 2 areelectrically connected.

In particular, and as shown in FIGS. 2 and 3, the P-type thermoelectricelements and the N-type thermoelectric elements, provided between thesame flow tube of the first fluid and the same flow tube of the secondfluid, may be associated with one another in such a way as to allow theflow of the current in series from one element of the first type to anelement of the second type. It is also possible to interconnect thesides of thermoelectric elements of the same type via electrical pathsfor a parallel assembly of said elements. The thermoelectric elements 4associated in this way form a base conduction cell and the cellsobtained may be associated in series and/or in parallel.

In these figures, the first contact side 3 a of each thermoelectricelement is intended to be in a heat exchange relationship with the hotchannel and the second contact side 3 b of each thermoelectric elementis intended to be in a heat exchange relationship with the cold channel.

The P-type thermoelectric elements alternate with the N-typethermoelectric elements. These two types of thermoelectric elements mayhave different coefficients of expansion. They are arranged in pairs,each pair being formed from one P-type thermoelectric elements and oneN-type thermoelectric element. The module is configured here to allow acurrent flow between the first contact sides 3 a of the thermoelectricelements of the same pair and a current flow between the second contactsides 3 b of each of the thermoelectric elements of two neighboringpairs. In other words, the current flows in series across thethermoelectric elements by passing alternately from a P-typethermoelectric element to an N-type thermoelectric element. For thispurpose, the module includes a plurality of electrical connection means20 connecting the first contact sides 3 a of the thermoelectric elementsof the same pair and to contact sides 3 b of each of the thermoelectricelements belonging to two neighboring pairs in order to allow thecurrent flow described above. Two adjacent thermoelectric elements areconnected by electrical connection means 20, either via their firstcontact side 3 a or via their second contact side 3 b. The assembly 30according to the invention entails the association of at least one ofsaid thermoelectric elements 4 and one of said electrical connectionmeans 20. Said electrical connection means 20 may also connect saidthermoelectric elements in series.

According to the invention, the connection means 20 can be connected totwo thermoelectric elements 4 via a single first element 41/secondelement 42 pair, as shown in FIG. 3, or two first element 41/secondelement 42 pairs can be used to connect the connection means 20, on theone hand, to a first thermoelectric element and, on the other hand, to asecond thermoelectric element.

As shown in FIGS. 4 and 5 a to 5 c, according to the invention, theassembly 30 includes a first deformable element 41 electrically linkingthe electrical connection means 20 to the thermoelectric element 4. Saidfirst deformable element 41 includes a first side 51 linked to theelectrical connection means 20 and a second side 52 linked to thethermoelectric element 4. Said first side 51 is deformable independentlyfrom said second side 52 and vice versa. The assembly furthermoreincludes a second deformable element 42, forming a heat bridge betweenthe first and second sides 51, 52 of the first deformable element 41.

The electrical connection means 20 may be in contact with a thermalconduction means, not shown, said thermal conduction means being anelectrical insulator. The thermal conduction means is made, for example,from ceramic material. It allows the transfer of heat between the coldchannel or the hot channel and the electrical connection means 20, whichthen transmits the heat to the thermoelectric element 4 on which it islocated via the first and second deformable elements 41, 42.

The thermal conduction means may be directly in contact with the coldchannel or the hot channel. It may also be in a heat exchangerelationship with the cold channel or the hot channel via thermalconduction fins to which it is applied.

The electrical connection means 20 includes, notably, electrical paths.They are made, for example, from copper, copper alloy, nickel or nickelalloy. The electrical connection means 20 furthermore includes asoldering material, referred to as solder, including, for example, andaluminum alloy. This solder is disposed, notably, in contact with theelectrical paths. It allows the connection means 20 to be soldered tothe thermoelectric element 4, notably via the first deformable element41. In other words, said first deformable element 41 is soldered to saidthermoelectric elements 4 and/or to said electrical connection means 20,notably via a plating or brazing sheet, disposed between the first side51 and the electrical connection means 20 and/or the second side 52 andthe thermoelectric element 4.

The first side 51 and the second side 52 are interconnected via twolateral walls 53. The first deformable element 41 thus forms aflat-sided tube, at least said first and second sides 51, 52 being flat.

In the example shown, the first deformable element 41 of the inventionis a sheet, notably folded to form the tube. It has a thickness of, forexample, between 50 μm and 300 μm. The sheet forming the first elementis made notably from metal and, in particular, aluminum or aluminumalloy. A sheet of this type notably has the advantage of being easilylocally deformable.

The invention also provides that the first deformable element 41 can bea grid. The structure of the grid improves the local deformationcapability of the first deformable element 41.

The second deformable element 42 is, for example, made of graphite. Thisnotably involves a sheet of graphite with a thickness of less than 1 mm.

The second deformable element 42 is located between the first side 51and the second side of the first deformable element 41, i.e. it is incontact with the first and the second side of the first deformableelement 41. It can thus form a heat bridge between the first side 51 andthe second side 52 notably in order to conduct heat between theconnection means 20 and the thermo-element 4. The second deformableelement 42 may also be in contact with the lateral sides 53. Here, thesecond element 42 fills the entire space 41 delimited by the first side51, the second side 52 and the lateral sides 53 of the first deformableelement 41, i.e. the entire inside of the tube formed by the firstdeformable element 41.

The second deformable element 42 is plastically and/or elasticallydeformable. Thus, as shown in FIG. 5, it can follow the deformations ofthe connection means 20 and of the first side 51 of the first deformableelement 41 independently from the deformations of the thermoelectricelement 4 and the second side of said first element 41.

These deformations are due, for example, to the expansions andcontractions which the connection means 20, the thermoelectric element 4and the assembly 30 undergo during their soldering and in operation athigh temperatures.

FIG. 5a shows the assembly of the invention at ambient temperaturebefore the soldering operation. The connection means 20, the firstdeformable element 41, the second deformable element 42 and thethermoelectric element 4 have their original dimensions.

In FIG. 5b , the assembly 30 is shown at soldering temperature, duringthe assembly of the connection means 20 with the first and seconddeformable elements 41, 42 and the thermoelectric element 4. Theconnection means 20, the first and second deformable elements 41, 42 andthe thermoelectric element 4 have then each undergone a differentthermal expansion as a function, notably, of their respectivecoefficients of thermal expansion. The assembly is then allowed tosolidify.

FIG. 5c shows the assembly 30 returned to ambient temperature while theconnection means 20 with the first element 41 and the thermoelectricelement 4 are soldered together. The connection means 20, the first andsecond elements 41, 42 and the thermoelectric element 4 have then eachundergone a different contraction as a function, notably, of theirrespective coefficients of thermal expansion.

It is then observed that the first and second deformable elements 41, 42have been deformed in such a way as to absorb the difference inretraction between the connection means 20 and the thermoelectricelement 4. They thus allow the deformations of the connection means 20to be mechanically decoupled from those of the thermoelectric element 4.The first side 51 of the first deformable element 41 has thus followedthe retraction of the connection means 20 and the second side 52 of thefirst deformable element has followed the retraction of thethermoelectric element 4. The side walls 53 have also been deformed,notably by tilting, to allow the first and second sides 51, 52 to bedeformed independently.

During this deformation of the first deformable element 41, the seconddeformable element 42 has followed this deformation, notably bycontinuing to occupy the entire inside of the tube defined by the firstdeformable element 41. It is thus able to provide a good heat conductionbetween the connection means 20 and the thermoelectric element 4.

The invention claimed is:
 1. An assembly comprising: at least onethermoelectric element for generating an electric current under theeffect of a temperature gradient exerted between two sides of the atleast one thermoelectric element, referred to as the contact sides; anelectrical connection means; a first deformable element electricallyconnecting the electrical connection means to the at least onethermoelectric element, the first deformable element including a firstside linked to the electrical connection means and a second side linkedto the at least one thermoelectric element, the first side beingdeformable independently from the second side and vice versa; a seconddeformable element forming a heat bridge between the first and secondsides of the first deformable element; a first soldering materialdisposed between the first side of the first deformable element and theelectrical connection means; and a second soldering material disposedbetween the second side of the first deformable element and the at leastone thermoelectric element.
 2. The assembly as claimed in claim 1, inwhich the first deformable element is a grid.
 3. The assembly as claimedin claim 2, in which the grid has a thickness of between 50 μm and 300μm.
 4. The assembly as claimed in claim 1, in which the first deformableelement is made of metal.
 5. The assembly as claimed in claim 1, inwhich the first and second sides of the first deformable element areinterconnected via two lateral sides in such a way that the firstdeformable element forms a flat-sided tube.
 6. The assembly as claimedin claim 5, in which the second deformable element fills a volumedelimited by the first side, the second side and the lateral sides ofthe first deformable element.
 7. The assembly as claimed in claim 1, inwhich the second deformable element is plastically deformable.
 8. Theassembly as claimed in claim 1, in which the second deformable elementis made of graphite.
 9. The assembly as claimed in claim 1, in which thefirst deformable element is soldered to the at least one thermoelectricelement and to the electrical connection means by the first solderingmaterial and the second soldering material, respectively.
 10. Theassembly as claimed in claim 1, including a second thermoelectricelement, having two contact sides, the second side of the firstdeformable element also being linked to the second thermoelectricelement.
 11. A thermoelectric module including a plurality of assembliesas claimed in claim
 1. 12. A thermoelectric device for generating anelectric current in a motor vehicle, including at least one module asclaimed in claim 11.